The present invention relates to a cover tape capable of being sealed to a polycarbonate carrier tape having pockets for containing electronic elements among packaging materials having functions of protecting electronic elements from contamination, arranging them for mounting on the surface of electronic circuit substrates and taking out them in storing, transporting and mounting the electronic elements.
Electronic elements to be surface-mounted, such as IC, transistors, diodes, condensers, piezoelectric resistors, etc. have been packaged with packaging materials comprising a plastic carrier tape having pockets regularly formed by embossing in conformity with the shape of the electronic elements, and a cover tape capable of being sealed to the carrier tape, and the resulting packages have been put to use. The electronic elements contained therein can be automatically taken out after peeling off the cover tape of the package, and can be surface-mounted on an electronic circuit substrate.
The mounting techniques have been yearly developed and are required to be high in precision of mounting, and it has been attempted to enhance production efficiency. Therefore, miniaturization of the elements to be mounted and speeding up of mounting have been rapidly spread, and as for the carrier tapes, decrease in width and increase in length thereof have been carried out. As materials of carrier tapes meeting the commercial demand, particularly polycarbonates have attracted public attention. This is because they are strong in rigidity and have heat resistance which can withstand heat sealing.
With decrease in width of carrier tapes, width of sealing trowel has been narrowed, and furthermore, with speeding up of mounting, the time for sealing to cover tapes has been gradually shortened to less than 1 second. Therefore, in order to obtain desired peel strength, the sealing temperature must be raised. Especially, sealing temperature for polycarbonate carrier tapes must be higher than sealing temperature for other plastic carrier tapes, and the heat sealing is carried out at about 200xc2x0 C. That is, sealing temperature must be changed depending on the materials of carrier tapes, which is one cause of reduction in production efficiency. Moreover, it is difficult to further raise sealing temperature and this is a problem which hinders speeding up of mounting operation.
The object of the present invention is to provide an electrically conductive cover tape which is excellent in transparency and can be heat-sealed, at a sealing temperature lower by at least 30xc2x0 C. than the presently employed sealing temperature even with narrow trowel width and shortened sealing time, to a polycarbonate carrier tape which has required a heat sealing temperature of about 200xc2x0 C.
The present invention relates to the following cover tapes.
(1) A cover tape for packaging electronic elements which can be heat-sealed to a polycarbonate carrier tape having regularly formed pockets for containing electronic elements, which cover tape comprises (A) a substrate layer comprising a thermoplastic resin having a load deflection temperature (ASTM D-648) under a load of 1.82 MPa of not lower than 60xc2x0 C., and (B) a heat seal layer comprising at least one resin selected from polyvinyl chloride resin, polyester resin, polyurethane resin, acrylic resin containing a functional group and ethylene copolymer which have a Tg of 30-60xc2x0 C., and an electroconductive fine powder dispersed in said resin.
(2) A cover tape for packaging electronic elements mentioned in (1), wherein the layer A has a thickness of 6-100 xcexcm and comprises polycarbonate, polyether sulfone, polyether imide, polyimide, nylon, polyester or polypropylene.
(3) A cover tape for packaging electronic elements mentioned in (1) or (2), wherein at least one layer selected from the group consisting of a polyester layer, a nylon layer, a polypropylene layer, a polyethylene layer and an ethylene copolymer layer is laminated between the layer A and the layer B.
(4) A cover tape for packaging electronic elements mentioned in (1), (2) or (3), wherein the comonomer of the ethylene copolymer mentioned in (1) and (3) is one member selected from the group consisting of vinyl acetate, acrylic acid, acrylate esters, methacrylic acid, methacrylate esters and ionomers.
(5) A cover tape for packaging electronic elements mentioned in (1), (2), (3) or (4), wherein the polycarbonate carrier tape has an electroconductive material incorporated and kneaded therein or coated on the surface of the tape.
(6) A cover tape for packaging electronic elements mentioned in (1), (2), (3), (4) or (5), wherein the electroconductive fine powder contained in the layer B consists of at least one member selected from tin oxide, zinc oxide, titanium oxide and carbon black, and the surface of the seal layer B has a resistivity of not more than 1xc3x971013xcexa9/xe2x96xa1.
(7) A cover tape for packaging electronic elements mentioned in (1), (2), (3), (4), (5) or (6) which has a total light transmittance of not less than 70% and a haze of not more than 60%.